the benq's im sorry to say but are problematic to say the least
try this...
1. unplug the monitor and flip it forward so its screen side down on a towel.
2. remove the screws from the back of the monitor and then take a flat head screwdriver and gently pry the back/front bezels apart.
3. after the back part and the front part are apart, look at front half of the bezel, there will be a Circuit board that is attached to it. follow the wire that is coming off the circuit board back to where it plugs in to the metal part.
4. firmly press the connector that at the end of that wire down into the connector.
5. put the monitor back together, and test the buttons.
if that does not work then you might have a serioulsy problem such as burnt component.
I’m happy to help further over the phone at
https://www.6ya.com/expert/paul_0af9b1d5c0eb4fc3